Reduction of agonist-induced contractions of guinea-pig isolated ileum by flavonoids

The effect of 13 flavonoids on the contraction of guinea-pig isolated ileum induced by prostaglandin E₂ (PGE₂) and leukotriene D₄ (LTD₄) have been investigated. Apigenin, quercetin and kaempferol at a concentration of 10 μM significantly (p<0.001) reduced the contraction to either agonist. Crysin and flavone antagonized only PGE₂ (p<0.01). The other flavonoids were inactive. The blocking effect of apigenin, quercetin and kaempferol against PGE₂ was also concentration- and time-dependent, and was augmented by the calcium channel blocker verapamil or by lowering the extracellular calcium to 25%, consistent with a calcium-mediated mechanism of protection which these flavonoids, at the same concentration, also showed against barium chloride (BaCl₂)- or acetylcholine (ACh)-induced contraction (p<0.05–0.001).